The aim of this work was to examine the improvement of anaerobic biodegradability of organic fractions of poplar leaf from codigestion with swine manure (SM), thus biogas yield and energy recovery. When poplar leaf was used as a sole substrate, the cumulative biogas yield was low, about 163 mL (g volatile solid (VS))−1 after 45 days of digestion with a substrate/inoculum ratio of 2.5 and a total solid (TS) of 22 %. Under the same condition, the cumulative biogas yield of poplar leaf reached 321 mL (g VS)−1 when SM/poplar leaf ratio was 2:5 (based on VS). The SM/poplar leaf ratio can determine C/N ratio of the cosubstrate and thus has significant influence on biogas yield. When the SM/poplar leaf ratio was 2:5, C/N ratio was calculated to be 27.02, and the biogas yield in 45 days of digestion was the highest. The semi-continuous digestion of poplar leaf was carried out with the organic loading rate of 1.25 and 1.88 g VS day−1. The average daily biogas yield was 230.2 mL (g VS)−1 and 208.4 mL (g VS)−1. The composition analysis revealed that cellulose and hemicellulose contributed to the biogas production.

•Continuous coal pyrolysis was studied in complex atmospheres at high temperatures.•At ER of 0.064 char had the highest specific surface area and oxidation reactivity.•In O2-free atmosphere the presence of CH4 and CO decreased char specific surface area.•Presence of H2 and CH4 condensed char crystallite structure to lower oxidation activity.The physiochemical properties of chars produced by coal pyrolysis in a laboratory-scale fluidized bed reactor with a continuous coal feed and char discharge at temperatures of 750 to 980 °C under N2-based atmospheres containing O2, H2, CO, CH4, and CO2 were studied. The specific surface area of the char was found to decrease with increasing pyrolysis temperature. The interlayer spacing of the char also decreased, while the average stacking height and carbon crystal size increased at higher temperatures, suggesting that the char generated at high temperatures had a highly ordered structure. The char obtained using an ER value of 0.064 exhibited the highest specific surface area and oxidation reactivity. Relatively high O2 concentrations degraded the pore structure of the char, decreasing the surface area. The char produced in an atmosphere incorporating H2 showed a more condensed crystalline structure and consequently had lower oxidation reactivity.

•Fluidization behavior of Geldart A particles in micro fluidized bed was simulated by CFD.•Minimum bubbling velocity and voidage predicted by Gibilaro model agreed with experimental data.•Solids-wall boundary conditions had substantial impact on flow behavior of gas and solids.The fluidization behavior of Geldart A particles in a gas–solid micro-fluidized bed was investigated by Eulerian–Eulerian numerical simulation. The commonly used Gidaspow drag model was tested first. The simulation showed that the predicted minimum bubbling velocities were significantly lower than the experimental data even when an extremely fine grid size (of approximately one particle diameter) was used. The modified Gibilaro drag model was therefore tested next. The predicted minimum bubbling velocity and bed voidage were in reasonable agreement with the experimental data available in literature. The experimentally observed regime transition phenomena from bubbling to slugging were also reproduced successfully in the simulations. Parametric studies indicated that the solid-wall boundary conditions had a significant impact on the predicted gas and solid flow behavior.

•It was possible to obtain similar RTDs in geometrically similar bubbling fluidized beds.•A simple scaling method was proposed without need of changing particle size and gas velocity.•RTDs of BFBs at different scales could be predicted by using the simple scaling method.Few studies have investigated scale-up of the residence-time distribution (RTD) of particles in bubbling fluidized beds (BFBs) with continuous particle flow. Two approaches were investigated in this study: first, using well-known scaling laws that require changes in particle properties and gas velocity; second, using a simple approach keeping the same particles and gas velocity for different beds. Our theoretical analysis indicates it is possible to obtain similar RTDs in different BFBs with scaling laws if the plug-flow residence time (tplug) is changed as m0.5, where m is the scaling ratio of the bed; however, neither approach can ensure similar RTDs if tplug is kept invariant. To investigate RTD variations using two approaches without changing tplug, we performed experiments in three BFBs. The derivatives dE(θ)/dθ (where E(θ) is the dimensionless RTD density function and θ is the dimensionless time) in the early stage of the RTDs always varied with m−1, which was attributed to the fact that the particle movement in the early stage were mainly subject to dispersion. Using the simple approach, we obtained similar RTDs by separately treating the RTDs in the early and post-stages. This approach guarantees RTD similarity and provides basic rules for designing BFBs.

Ni–Mg/Al2O3 catalysts prepared with methods of co-precipitation (CP), homogeneous precipitation (HP) and acid–base pairing (ABP) were tested for syngas methanation at 623–923 K in a stainless steel fixed bed reactor and further characterized to justify their performances. The Ni–Mg/Al2O3 catalysts prepared with CP using NH4OH, NaOH and Na2CO3 as the precipitants followed an activity order of NaOH > NH4OH > Na2CO3. Comparing further with the samples prepared by HP and ABP resulted in an activity order of HP > ABP > CP (NaOH) for syngas methanation under 0.1 MPa. For CO conversion, a transition of reaction control from kinetic dominance to thermodynamic dominance was observed at about 780 K. Performing 20 h continuous tests at 773 K and under 0.1 and 2.5 MPa further verified the stability of the HP, ABP and CP (NaOH) catalysts for syngas methanation. Analyzing the catalysts via H2-TPR clarified that a lower amount of free NiO and a stronger interaction between the dispersed NiO and Al2O3 or MgO ensured better catalytic performance for methanation. The study also identified two types of carbon deposited on the surface of the spent catalysts.

•Dual-stage fixed bed was used to study catalytic upgrading of coal pyrolysis tar.•Tested catalysts were char and char impregnated with CoCl2, NiCl2, CuCl2 and ZnCl2.•Char catalyst leaded to higher light tar fraction and little changed light tar yield.•Metal-char catalyst was more effective than char for upgrading coal pyrolysis tar.•Of the tested catalysts the Ni-char catalyst showed the best tar upgrading effect.Catalytic upgrading of coal pyrolysis tar was investigated in a dual-stage reactor over char and metal-impregnated char (Co-char, Ni-char, Cu-char, Zn-char). The catalytic upgrading caused the lower total tar yield and the higher non-condensable gas yield but the fraction of light tar (boiling point < 360 °C) obviously increased to allow slightly higher total yield of light tar. When the catalytic upgrading was at 600 °C over a layer of char having a mass of 20% of the tested coal, the resulting light tar fraction in the tar increased by 25% in comparison with the coal pyrolysis only at 600 °C. Over the metal-impregnated char, which was 5% of the tested coal in mass, good upgrading effect was obtained at 500 °C. The catalytic tar-upgrading activity decreased in an order of Co-char > Ni-char > Cu-char > Zn-char, and over Ni-char the realized light tar yield and its content in the tar increased by 17.2% and 32.7%, respectively. The upgrading effect also lowered the contents of element N and S in the resulting tar by 45.6% and 43.5%, respectively. NH3-TPD clarified that the order in acidity of the char-based catalysts was the same as for the upgrading activity shown above.This figure compares the fraction and yield of light tar (boiling point < 360 °C) obtained from coal pyrolysis under the conditions without (Blank) and with secondary catalytic upgrading over various char-based catalysts. In comparison with the pyrolysis without secondary upgrading, the adoption of the secondary upgrading all evidently increased the light tar fraction, while only the catalysts impregnated with metal species caused obvious increase in the light tar yield. The Ni-char catalyst showed the best upgrading effect, and next to this was the Co-char catalyst. These results demonstrated that the secondary catalytic upgrading greatly improved the tar quality, and this would greatly facilitate the downstream treatment for the tar.

•We investigate NO reduction characteristics by biomass tar compared with char.•Reduction efficiency was studied upon the micro-fluidized bed reaction analyzer.•Reduction efficiency over the same mass of agent is higher for tar than for char.•Five model compounds further clarify reduction capability of single tar component.•The kinetics parameters were estimated by the isothermal differential approach.The so-called micro-fluidized bed reaction analyzer (MFBRA) that enables the evaluation of rapid chemical reactions was used to investigate the NO reduction characteristics by biomass tar agent in terms of its activity and efficiency for reducing NO. Biomass char was used as a comparative reduction agent in this study. The employed biomass tar and char were made from pyrolyzing distilled spirit lees (DSL), a massive fermentation waste generated in China. The results showed that the NO reduction defined for the same mass (10 mg) of reactant was more efficient for tar than for char. The identified peak NO reduction efficiency (inlet: 1800 ppm) was high as 73.8% for 10 mg tar but only 39.3% for the same amount of char. Testing the NO reductions by five typical model tar compounds including acetic acid, toluene, phenol, naphthalene and 1-hydroxy-naphthalene demonstrated that all these components contributed to the capability of tar for NO reduction. The article estimated as well the kinetic parameters of NO reduction by tar based on the MFBRA-measured data according to the isothermal differential approach, finding that the apparent activation energy of NO reduction reaction by tar was 122 kJ/mol.

Intrinsic fundamentals of catalytic tar removal over coal char were studied in a laboratory two-stage gasification facility. The in situ char from coal pyrolysis (without cooling) exhibited higher activity for tar removal than the char experiencing its slow cooling in N2 to room temperature. The tar content in dry producer gas can be as low as 100 mg/Nm3 over the in situ char in 1.2 s of gas residence time inside the char bed at 1100 °C. Brunauer–Emmett–Teller surface area results showed that the in situ char has a larger specific surface area and more micropores than the ex situ char, while X-ray diffraction analysis clarified that the ordering of the carbon crystallite structure in the char increased with raising the temperature of tar removal. The latter is considered to be due to the facilitated secondary pyrolysis occurring to the ex situ char at increased temperatures. The secondary pyrolysis of the ex situ char also decreased its specific surface area and the amount of micropores. Severe coke deposition on the surface of spent char was observed, especially at temperatures above 1000 °C. The tar coking ratio defined as the mass ratio of coked tar over the totally converted tar reached as much as 0.7 when the temperature was 1100 °C and the gaseous tar residence time was 1.2 s. The coke formed on the char surface reduced the difference of structural properties between the in situ and ex situ chars and, in turn, decreased the difference in their performances for cracking tar.

•Highlights•Flow regimes were identified in the TFB without a gas distributor.•The gas-solid flow characteristics in the fluidized bed were clarified.•Models were modified to predict the hydrodynamic characteristics of the bed.The tapered fluidized bed (TFB) without a gas distributor has long been used as an atmospheric coal gasifier by taking advantage of its simplicity in configuration and maintenance and also its ease in discharging bottom ash. This study investigated the hydrodynamic characteristics of such a bed fluidizing quartz sand of 156 μm in mean diameter to understand if it enables the fully uniform fluidization of its particle bed. The changes in pressure drop and voidage in the bed were measured under varied conditions. Three flow regimes were identified by gradually increasing the superficial gas velocity through the bed. The gas–solid flow in the bed can be divided vertically into three gross sections of gas convergence, gas diffusion and particle elutriation, and laterally into two zones of annulus and core. Vertically along the bed the shape of the radial voidage profile changed gradually from an “M” shape to a “parabola” by increasing the superficial gas velocity from 0.17 m/s to 0.35 m/s. The axial voidage profile at the bed center showed the “S” shape to distinguish the above-mentioned three vertical sections. These indicated the existence of non-uniformity of particle fluidization in the bed, and changing the arrangement of gas jets into the bed did not fully resolve the problem. The article found also that the major hydrodynamic parameters of the tested TFB using only one layer of gas jet to supply the fluidizing gas could be predicted by modifying their empirical correlations known for the TFB with a gas distributor.The figure illustrates the typical gas flow features in the TFB without a gas distributor. Based on the directions of the gas flow and gas–solid interaction forces, the TFB above the nozzles can be divided vertically into a “convergence section”, a “diffusion section” and an elutriation section. In the convergence section, the directions of gas flow and gas–solid interaction force are mainly horizontal while these are mainly vertical in the diffusion section. There are also an annulus near the bed wall where the particles move downward with small voidage and a dead hill below the gas convergence point or a part of the bed between the nozzles where the particles are in compact packing state and the gas from the nozzles cannot get through.

This study is devoted to characterizing the isothermal reaction kinetics of char gasification with CO2 in a micro fluidized bed reaction analyzer (MFBRA) in comparison to the measurement in a thermogravimetric analyzer (TGA). Under minimized inhibition of heat and mass transfer, the reaction rate was found to be much higher in the MFBRA than in the TGA. The maximal rate appeared at a conversion of about 0.15 in the MFBRA but at 0.45 in the TGA. The shrinking core model described well the char–CO2 gasification reaction in both the MFBRA and TGA. In the temperature range of 760–1000 °C, the char–CO2 gasification reaction can be divided into two stages. At lower temperatures, the activation energy from the MFBRA and TGA is very close, validating the reliability of the MFBRA for analyzing gas–solid reaction kinetics. At higher temperatures, the estimated activation energy was obviously higher for the MFBRA than for the TGA, showing the lower diffusion limitation prevailing in the MFBRA. The frequency factor for the Arrhenius equation was found to be much higher for the MFBRA than for the TGA, complying with the higher reaction rate observed in the MFBRA. The variation in the reaction atmosphere composition during gas switching in the TGA was also investigated.

With utilization of internals to enhance heat transfer and regulate the pyrolysis gas flow direction inside the reactor, this study proposed and tested a new fixed-bed coal pyrolysis reactor indirectly heated. Majorly, both yield and quality of the produced tar were evaluated by comparing the behaviors of laboratory pyrolyzers with and without internals. The results show that the use of the particularly designed internals increased the heating efficiency from the reactor wall to the coal bed by more than 2 times, while the tar yield was obviously higher in the reactor with internals. For Yilan sub-bituminous coal, the tar yield reached about 80% of the tar yield given by the Gray–King analysis (11.8 wt %, dry-coal basis) in the laboratory reactor with internals, while the corresponding light tar below the boiling points of 360 °C was about 65 wt % of the total tar mass. With raising the heating temperature of the furnace from 600 to 1000 °C, the tar yield increased from 8.5 to 10.64 wt % for the reactor with internals. In contrast, the tar yield decreased remarkably from 7.98 to 4.77 wt % in the conventional reactor without any internal. All of these show essentially that the adopted internals greatly changed the physiochemical procedure involved in coal pyrolysis, which, in turn, obviously affected the yield and quality of tar.

•Destruction of caking propensity of coal by jetting pre-oxidation was tested in a laboratory fluidized bed.•Caking destruction was well achieved for a kind of coal with a caking index of 20.•Oxidation temperature and oxygen content in jetting gas are essential to the caking destruction.•Variations in bed temperature and product gas composition are indicative of caking condition in the bed.Jetting pre-oxidation was proposed to destroy the caking property of bituminous coal in a fluidized bed (FB) gasifier. By defining an index ω to characterize the degree or realized effect of caking destruction, experiments were conducted in an electrically heated laboratory FB reactor under different conditions to investigate the feasibility and required conditions for effectively destroying the caking propensity of a kind of bituminous coal. The tested major parameters were the equivalence air ratio (ER) of jetting gas and the temperature in the jetting zone. At relatively lower temperatures it was hard to completely destroy the caking propensity of the tested coal particles. Without oxygen inside the jetting gas, it was also impossible to fully destroy the caking propensity of the coal even at sufficiently high temperatures. Thus, oxidation of coal particles at suitably high temperatures was essential to the expected good destruction of their caking propensity. For the tested bituminous coal this was achieved at temperatures above 1000 °C in the jetting zone and an equivalent oxygen ratio above 0.1 for the jetting gas (up to 0.3 considering gasification applications). For coal pre-oxidation in a FB, the agglomeration state of char particles due to caking adherence in the reactor could be anticipated via the unsteady variations in the bed temperature and H2/CO concentrations in the effluent gas with reaction time.

•VOx/graphene hybrid materials were fabricated using a simple hydrothermal method.•The performance of VOx–n% GO-T is affected by GNS content and annealing temperature.•The VOx–7.4% GO-300 composite electrode shows superior capacitive properties.•The excellent performance is attributed to the improved dispersion and utilization.The vanadium oxides (VOx)/graphene hybrid materials constructed from 2D graphene nanosheets (GNS) and VOx are successfully prepared by a simple two-step procedure including solvothermal method and subsequent thermal treatment. Effects of the GNS content and the annealing temperature on the microstructure and morphology of as-obtained composites are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Importantly, the electrochemical properties of as-prepared composites are systematically investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy, which are highly dependent on the content of GNS in composite and the annealing temperature. Furthermore, the VOx–7.4% GO-300 composite electrode exhibits the largest specific capacitance and the most excellent rate capability among these composites. These encouraging results illustrate the exciting potential for high performance energy storage devices based on the VOx–7.4% GO-300 composite.

•Residue cracking combined coke gasification was proposed for heavy oil utilization.•A catalyst (BFC) with both cracking and gasification activity was synthesized.•Hydrothermally treated FCC and BFC had suitable catalysis for heavy oil cracking.•The BFC showed higher activity for coke gasification than FCC.•Both FCC and BFC had good stability in regeneration by steam coke gasification.The so-called petroleum residue cracking gasification (RCG) process intends to convert the heavy oil first into cracked liquid by catalytic cracking and then into syngas via catalytic gasification of the cracking-formed coke. A bifunctional catalyst (BFC) was synthesized in this article and tested for the petroleum residue cracking gasification in a laboratory-scale fluidized bed reactor through comparison with the performance over an FCC catalyst. Low liquid yield of vacuum residue (VR) cracking was obtained with fresh BFC and FCC catalysts because of their strong acidity and thus activity. Hydrothermal treatment was thus performed to weaken the acidity of both the catalysts. This resulted in liquid yields of about 80 wt.% at 500 °C for cracking the same VR. The spent BFC and FCC catalysts were both in situ regenerated via steam gasification of the formed coke in the same fluidized bed reactor. This generated simultaneously syngas which contained CO and H2 of up to 80 vol.%, and the realized carbon conversion was over 95% at 800 °C for both the catalysts. However, the regeneration time for BFC was greatly shorter than that for the FCC catalyst. This shows the much better activity of BFC for coke gasification in comparison with FCC that has almost no activity for catalyzing coke gasification. In fact, the BFC contained much more active alkaline metal sites than the FCC to ensure its catalytic activity for gasification.

Even at present it is still difficult to characterize the reaction between CO2 and Ca(OH)2 at high temperature and atmospheric pressure using traditional instruments such as thermogravimetric analyzer and differential scanning calorimeter. This study was devoted to characterizing such a reaction in a newly developed micro fluidized bed reaction analyzer (MFBRA) under isothermal conditions in the temperature range of 773–1023 K. The results indicated that the MFBRA has not only a good adaptability for characterizing the above-mentioned reaction but enables as well a new insight into the mechanism of the reaction. An obvious time delay was identified for the release of the formed steam (H2O) in comparison with the onset of its CO2 absorption, which might be attributed to the formation of an unstable intermediate product Ca(HCO3)2 in the reaction process between CO2 and Ca(OH)2. The activation energy for forming Ca(HCO3)2 was found to be about 40 kJ/mol, which is much lower than that of the reaction between CO2 and CaO.

•Multi-stage fluidized bed pyrolysis was tested to upgrade lignite and coproduce tar.•The yields of gas and tar were higher for multi-stage fluidized bed pyrolysis.•The tar from multi-stage fluidized bed pyrolysis contained more light oil.•The char from multi-stage fluidized bed pyrolysis had higher thermal stability.•Multi-stage bed pyrolysis has obvious technical advantages for lignite upgrading.This study is devoted to demonstrating experimentally the technical advantages of the multi-stage fluidized bed pyrolysis for upgrading lignite. A Chinese lignite was pyrolyzed and partially gasified in a three-stage laboratory-scale fluidized bed, with an overflow standpipe between its neighboring stages, to clarify the improvement on the pyrolysis product quality by increasing the number of the stages. While the bottom stage had the highest temperature of about 900 °C for fuel gasification, the upper stage had temperatures of 550–650 °C for coal pyrolysis. The multi-stage fluidized bed was operated with a continuous feed in the modes with one to three stages. The resulting yields of gas and tar were higher, whereas the yield of char was lower for the operations with multiple stages. The produced CO, H2 and CH4 in the two- and three-stage modes were more than that in the single-stage mode, having thus the higher gas heating value as well. The tar from the three-stage fluidized bed pyrolysis contained more light oil, and it plus phenol oil reached 99.5 wt.% of the tar. The char produced in the multi-stage pyrolysis showed the higher thermal stability in terms of its higher ignition temperature and suppressed spontaneous combustion propensity.This figure compares the product distribution obtained in pyrolyzing a kind of Chinese lignite in fluidized beds with one to three stages, showing that increasing the number of stages from one to three dramatically increased the pyrolysis gas yield from 45.9 wt.% to 87.8 wt.%. The tar yield slightly increased from 1.5 wt.% to 2.8 wt.%, whereas the char yield decreased from 54.8 wt.% to 36.3 wt.%. Thus, increasing the number of operation stages facilitated the pyrolysis reactions at their suitable temperatures by having longer reaction time, while on the other hand, the produced tar has low possibility to be cracked at high temperatures.

The thermochemical conversion process of solid fuels is explicitly shown as the processes of pyrolysis (including coking and carbonization), gasification, and combustion. These processes actually involve a similar complex reaction network. The so-called “decoupling” refers to the optimization approach of process performance through controlling the interactions between or among the involved individual reactions. Our previous article in Energy & Fuels (2010, 24, 6223–6232) has analyzed how the approach of decoupling applies to the gasification technologies and justified the realized effects from decoupling. This successive report is devoted to understanding the applications of decoupling to the other types of thermochemical conversion technologies (mainly including pyrolysis and combustion) so as to generalize the “decoupling” methodology for innovations of thermochemical conversion technologies. After a reiteration of the principle and implementation approaches (isolating and staging) for decoupling, reanalysis of the process design principle and its consequent technical superiorities based on decoupling is performed for a few well-known or emerging novel conversion technologies developed in the world. The concrete technologies exemplified and their realized beneficial effects include the high-efficiency advanced coal coking processes with moisture control or gentle pyrolysis of feedstock in advance, coal pyrolysis in multiple countercurrent reactors for producing high-quality tar, gasification of caking coal in fluidized bed through adopting jetting preoxidation of coal, low-NOx decoupling combustion of coal by developing the in-bed NOx reduction capabilities of pyrolysis gas and char, and coal topping combustion for the coproduction of tar and heat. These highlights further justified that the decoupling would be a viable technical choice for achieving one or more of the technical advantages among polygeneration, high efficiency, high product quality, wide fuel adaptability, low pollutant emissions in thermochemical conversions of solid carbonaceous fuels.

Many fuel conversion technologies using dual fluidized bed (DFB) have been developed, including the chemical looping combustion (CLC), CO2 acceptor, and DFB pyrolysis or gasification of biomass and coal. In this kind of system, solid particles are circulated between two fluidized bed (FB) reactors to carry heat or a specified chemical element from one reactor to the other. Thus, a special matching in heat and mass as well as its control is critical to the involved reactors and their integrated system. This paper is devoted to reviewing the recent progress on chemical engineering fundamentals particularly about the DFB fuel pyrolysis and gasification systems in terms of technical process, reactor and auxiliary equipments development, and bed material and reaction control. While the first aspect covers the optimization of reactor combination, process simulation, and hydrodynamic and kinetic modeling, the second part includes the optimization of reactor structure, realization of high particle circulation rate, and integration of reactor with siphon. The highlights in the third aspect are about the pretreatment of fuel and the choice of bed material in the view of intensifying reactions and upgrading products. It is expected that this Review not only summarizes the related studies but gains also an understanding of the DFB pyrolysis and gasification systems from an alternated viewpoint.

This study is devoted to developing a continuous activated carbon (AC) production process integrating drying, carbonization, and physical activation without external heat input. The massive byproduct in the distilled spirit industry, distilled spirit lees (SL), was used as the raw material in this study. The kinetic behaviors in each step, including drying, carbonization, and activation, were first investigated via laboratory tests. The results show that the whole AC production process can be completed in 30 min, including most of the time for drying, several minutes for carbonization, and several seconds for activation. On the basis of these laboratory results, an integrated process for continuous production of AC was proposed. The mass and heat balance calculation demonstrated a good balance for the developed process technology, and a pilot plant treating 2000 kg of SL/h was in turn built and commissioned to run autothermally and continuously. This demonstrated thus the technology for application to granular feedstock such as SL, although the produced AC from SL had surface areas of only about 191 m2/g and relatively low adsorption values, including 610–630 mg/g for iodine and 20–30 mg/g for methylene blue, due to the too short activation time in the pilot activator.

Via isolating the fuel pyrolysis and char gasification, the so-called dual bed pyrolysis gasification (DBPG) was proposed to realize the co-production of pyrolysis products and gasification gas. The process simulation with Aspen Plus shows that the DBPG process can run autothermally using air as the gasification reagent, but the complete conversion of char in the gasifier requires relatively high O/C ratio due to the absence of steam in the reactor. This would make the higher heating value (HHV) of the produced gasification gas below 1000 kcal/Nm3. Adding steam to the char gasifier can realize full char conversion at lower O/C ratio to improve the gasification gas quality. The effect of air preheating on the gasification performance was further analyzed to optimize the operating conditions of DBPG. A pilot scale plant (100 kg-coal/h) of DBPG was established and tested by using air as the gasification reagent plant to verify the technology feasibility. At the steady operating temperatures of 600 °C for pyrolyzer and 850 °C for gasifier, the produced pyrolysis gas was rich in hydrocarbons and the tar yield reached 8.4 wt% and was rich in phenols and its derivatives, but the HHV of the gasification gas was only 510 kcal/Nm3, much lower than the simulated value. A laboratory test on char–air gasification in a fluidized bed reactor further showed that the short residence time of char inside the gasifier and thus the low carbon conversion and the burning of the produced gas in the reactor was the cause for this lower heating value of the gasification gas.Highlights► Isolating fuel pyrolysis and char gasification reactions via dual-bed technology. ► Process feasibility was studied by process simulation and a pilot test of 100 kg/h. ► Process simulation justified the technology feasibility. ► Pilot test featured the products of tar, pyrolysis and gasification gas.

Through separating coal pyrolysis and char combustion and letting the pyrolysis gas burn in its passing through the combusting char bed, the so-called decoupling combustion has been proven to be effective for lowering NOx emission of coal and biomass combustion. The original design of the decoupling combustion was based on coal pyrolysis incurring with the heat transferring from the char combustion zone, thus causing the difficulty of scale-up in matching the reactions of slow coal pyrolysis and quick char combustion. An idea of using partial gasification to replace such a pyrolysis was proposed to allow the combination of reburning part of the gasification gas over the combusting char layer and the decoupling combustion of the left gasification gas by letting it pass through the char bed. This article compared first the effectiveness of reducing NOx emission by a few different combustion methods including reburning of gasification gas and the decoupling combustion based on coal pyrolysis in a laboratory scale dual-stage reactor for five different kinds of coal. It was shown that both the decoupling combustion and reburning of gasification gas represented the most effective low-NOx combustion methods, which can reduce the NOx emission by 30–40% in comparison with the traditional combustion without air-staging and reburning. The fuel ratio of fixed carbon to volatile matters of the coal also affected the effectiveness of NOx reduction, the lower the fuel ratio, the higher the NOx reduction effect was. The actual running test of a 1.4 MW industrial boiler based on combining the decoupling combustion and reburning part of the partial gasification gas reduced the NOx emission by 33% in comparison with the traditional industrial boiler. The result showed a successful scale-up of the technology and verified the idea of reducing NOx emission by combining the decoupling combustion and the reburning of coal gasification gas.Highlights► Low-NOx emission is realized by combining decoupling combustion and gas reburning. ► Performances of decoupling combustion and gasification gas reburning were evaluated. ► Above 33% NOx emission can be reduced in decoupling combustion process. ► A 1.4 MW boiler was developed based on the principle of decoupling combustion and gas reburning.

This study is devoted to investigating the continuous coal pyrolysis in a laboratory fluidized bed reactor that fed coal and discharged char continuously at temperatures of 750–980 °C and in N2-base atmospheres containing O2, H2, CO, CH4 and CO2 at varied contents. The results showed that the designed continuous pyrolysis test provided a clear understanding of the coal pyrolysis behavior in various complex atmospheres free of and with O2. The effect of adding H2, CO, CH4 or CO2 into the atmosphere on the tar yield was related to the O2 content in the atmosphere. Without O2 in the atmosphere, adding H2 and CO2 decreased the pyrolysis tar yield, but the tar yield was conversely higher with raising the CO and CH4 contents in the atmosphere. In O2-containing atmospheres, the influence from varying the atmospheric gas composition on the product distribution and pyrolysis gas composition was closely related to the oxidation or gasification reactions occurring to char, tar and the tested gas.Highlights► Coal pyrolysis behaviors were studied in fluidized bed with continuous coal feed and char discharge. ► The yields of product were obtained in complex atmospheres at temperatures from 750 °C up to 980 °C. ► Raising the ER until 0.107, tar and char yields decreased, while gas and water yields increased. ► In O2-free atmosphere, adding CH4 into the atmosphere increased tar and char yields. ► Adding combustible gas into the N2 + O2 atmosphere increased the tar and char yields.

Activated carbon (AC) was prepared from ash-rich distilled spirit lees via carbonization and successive activation incorporated with different deashing methods. The results show that the alkali treatment of the steam-activated carbon (ATAC) produced the AC with the highest performance in comparison with the NaOH activation and direct alkali treatment of the carbonized carbon (ATCC). The ATAC removed 84.4% of the ash from steam-activated carbon and increased the BET surface area and total pore volume by 92.3% and 109.3%, respectively, resulting in the AC with its ash content of 11 wt %, BET surface area of 620 m2/g, and total pore volume of 0.67 cm3/g. The article also revealed that it is possible to use the alkaline leaching solution from the ATAC, which is mainly composed of sodium silicate, as the major binder to mold the produced powder AC.

Vacuum residue (VR) was stepwise converted via catalytic cracking for liquid and coke gasification for hydrogen-rich syngas in a fluidized bed reactor. Silica sand and spent equilibrium FCC (E-FCC) catalyst were used as the catalysts for VR cracking. The liquid yield was about 89 wt % at 568 °C using silica sand as catalyst and the conversion ratio of heavy fractions was only 55%. About 60 wt % VR was converted into gas and coke over the E-FCC catalyst at 480 °C, showing that the catalyst had too strong acidity for VR cracking. The E-FCC catalyst was thus modified (aged) with both hydrothermal treatment and impregnation of alkali and alkaline-earth metals (K and Mg) to weaken its acidity and facilitate the liquid oil production. The aged FCC (A-FCC) catalyst exhibited appropriate cracking activity to allow both the expected liquid yield of about 80 wt % and heavy fraction conversion ratio of up to 98 wt %. Steam gasification of the deposited coke on the surface of the A-FCC catalyst resulted in the production of syngas containing CO and H2 content to be about 45 and 42 vol %, respectively.

It is reasonable to speculate the adaptability of Horio's scaling law (equivalent to the simplified Glicksman's scaling law) to the particle mixing and segregation behavior in bubbling fluidized bed (BFB), because the Horio's scaling law is derived from the governing equations of bubbles, and the particle mixing and segregation are dependent on bubble dynamics. In this study, several experiments under various conditions were performed to verify the adaptability of Horio's scaling law. The experimental results indicate that the Horio's scaling law can be successfully applied to mixing and segregation behaviors of Geldart B particles in BFB under the conditions studied in this paper if the scaling relations are strictly satisfied, which is expected to be helpful in the design of fluidized bed reactor.Comparisons of the particle segregation behavior between two bubbling fluidized beds under various conditions (mi denotes mixing index which is zero at totally segregation state and equal to 1 at the perfectly mixing state).Highlights► Particle mixing similarity in BFBs is obtained if scaling law relations are fulfilled. ► Adaptability of scaling law to the particle mixing in BFBs is verified. ► Gas velocity and bed height have significant impacts on particle mixing behaviors.

Coal moisture control (CMC) in coking process, which reduces coal moisture before loading the coal into the coke oven, allows substantial reduction in coking energy consumption and increase in coke productivity. The technology is seeking to integrate the coal classification, thus calling it the coal classifying moisture control (CCMC), to separate the fine and coarse coal fractions in the CMC process so that the downstream coal crushing can only treat the coarse fraction. CCMC adopts a reactor that integrates a fluidized bottom section and a pneumatic conveying top section. The present work investigates the pneumatic classification behavior in a laboratory CCMC reactor with such a configuration by removing the coal fraction below a given size (e.g., 3.0 mm) from a 0 to 20.0 mm coal feed. The results show that the coal classification were dominated by the gas velocity in the top conveying section, and the required gas velocity for ensuring the maximal degree of removing a fine coal fraction could be roughly predicted by the Richardson and Zaki equation. The effect of bottom fluidization on the performance of CCMC is also examined.Graphical abstractClassification performance as a function of gas velocity.Highlights► The tandem fluidized bed elutriator integrates a fluidized bottom section with a pneumatic conveying top section for separating fine coal smaller than 3.0 mm from larger particles. ► Classification performance is subject primarily to the gas velocity in the pneumatic conveying section. ► Adopting small-diameter bottom, lowest possible particle bed height and secondary gas stream help improve classification performance.

An effective technology for utilizing vinegar lees (VL), a biomass waste generated during its production, is much needed in China due to the huge consumption of vinegar. This study investigates the preparation of porous carbon (PC) from VL, now reporting on the adsorption capability of PC in removing phenol from its aqueous solution. The preparation of PC consists of carbonization of VL in N2 and activation in CO2. The results show that the optimal activation temperature and time in CO2 for VL char carbonized at 800 °C were 875 °C and 1 h, respectively. The PC prepared was found to have large specific surface area and micropore volume, with an adsorptive capacity for phenol from its aqueous solution much higher than that of commercial coconut shell activated carbon (CSAC). Adsorption of phenol from its aqueous solution by the VL-based PC was found to follow the isothermal Langmuir equation.The optimal conditions for preparing porous carbons (PCs) with high specific surface area were: carbonization at 800 °C for 1.0 h in N2 followed by activation at 875 °C for 1.0 h in CO2. The PC thus prepared has higher adsorptive capacity than commercial coconut shell activated carbon for phenol removal from its aqueous solution.

Simulating the conditions of pyrolytic topping in a fluidized bed reactor integrated into a CFB boiler, the study was devoted to the reaction fundamentals of coal pyrolysis in terms of the production characteristics of pyrolysis oil in fluidized bed reactors, including pyrolysis oil yield, required reaction time and the chemical species presented in the pyrolysis oil. The results demonstrated that the maximal pyrolysis oil yield occurred on conditions of 873 K, with a reaction time of 3 min and in a reaction atmosphere gas simulating the composition of pyrolysis gas. Adding H2 and CO2 into the reaction atmosphere decreased the pyrolysis oil yield, while the oil yield increased with increasing the CO and CH4 contents in the atmosphere. TG-FTIR analysis was conducted to reveal the effects of reaction atmosphere on the chemical species present in the pyrolysis oil. The results clarified that the pyrolysis oil yield reached its maximum when the simulated pyrolysis gas was the reaction atmosphere, but there were slightly fewer volatile matters in the pyrolysis oil than the oil generated in the N2 atmosphere. All of these results are expected not only to reveal the composition characteristics of the pyrolysis oil from different conditions of the coal topping process but also to optimize the pyrolysis conditions in terms of maximizing the light pyrolysis oil yield and quality.

Distilled spirits Lees, rich in cellulose, water and N element, are difficult to burn efficiently and cleanly in grate chain stock boiler. The circulating fluidized bed decoupling combustion (CFBDC) was therefore proposed to burn the distilled spirits lees efficiently and with low-NOx emission. The pyrolysis behavior of the distilled spirits lees was investigated in a fluidized bed reactor for optimizing the pyrolysis conditions of the pyrolyzer in CFBDC. The results showed that the distilled spirits lees began to devolatize at 250 °C and at 350–450 °C the tar yield reached its maximum of about 16.3 wt.% (dry base). The chemical oxygen demand (COD) value of the condensed liquid reached its maximum of about 50,000 mg/L at 450 °C. With raising temperature the pyrolysis gas tended to contain more CO and H2 and less CO2. The functional groups H-O, aliphatic C-H, aromatic ring, C=O and C-O were all presented in the char generated at low-temperatures, while only the C-O group was identified for the char from the pyrolysis at 650 °C. The article suggested that the pyrolysis for the CFBDC was better around 500 °C so that certain volatiles could remain in the char to sustain stable combustion.Highlights► The pyrolysis of distilled spirits lees was investigated in a fluidized bed. ► At 350–450 °C the tar yield reached its maximum of about 16.3 wt.%. ► With temperature rising the pyrolysis gas contained more CO, H2 and less CO2. ► Most functional groups in char disappeared at high-temperature, such as 650°C.

Coal pyrolysis is generally performed in atmospheres without oxygen and at temperatures below 650 °C for producing pyrolysis liquid and gas. To support the development of a new two-stage gasification process integrating a fluidized-bed pyrolyzer and a downdraft fixed-bed gasifier, this paper investigated the coal pyrolysis in atmospheres containing oxygen and steam and at temperatures up to 900 °C to understand the viable pyrolysis conditions in view of process adaptation. The examined pyrolysis characteristics include the product distribution, char gasification reactivity, and tar composition. The pyrolysis gas yield, especially the yields of H2 and CO, increased with elevating the temperature and mass ratio of steam/coal (S/C). Adding O2 to the reaction atmosphere promoted the formation of CO and CO2 but decreased that of H2. The inclusion of O2 and steam in the atmosphere resulted in chars with a larger surface area and more micropores. At 900 °C in N2 atmosphere or at 850 °C with oxygen in the atmosphere (e.g., at an excessive air ratio of 0.22), graphitization was observed in the produced char, which lowered the char gasification reactivity. Analyzing the produced tar via thermogravimetry coupled with Fourier transform infrared (TG−FTIR) spectroscopy clarified that the presence of steam significantly affected the tar composition by leading to more aliphatic hydrocarbons and lowering the contents of single-ring aromatics, phenols, and ketonic species. Thus, the pyrolysis gas product from a steam-containing reaction atmosphere would be easier to crack and be reformed in the downstream char gasifier.

A new two-stage gasification process, consisting of a fluidized-bed (FB) pyrolyzer and a downdraft fixed-bed (DFB) gasifier, has been proposed to gasify powder coal for fuel gas production with low tar generation. Aiming at developing the new technology, this paper investigated the means for coal pyrolysis gas upgrading, with the focus on tar removal by both thermal cracking with or without the presence of oxygen and catalytic cracking or reforming over a char bed in a fixed-bed reactor downstream of a FB coal pyrolyzer. The presence of oxygen and the adoption of a char bed evidently facilitated the tar removal performance and also improved the produced fuel gas quality. Analyzing the tar sample collected at the outlet of the tar removal reactor with gas chromatography–mass spectrometry (GC–MS) clarified that the oxidation by O2 and the char-catalyzed reforming both exhibited certain selectivity to the tar-containing chemical species. In addition, the property of char played an important role on its catalytic activity. The higher the specific surface area, the better the activity of char for removing tar. The spent char showed a much reduced specific surface area of micropores but evidently elevated the specific surface area of mesopores, even by up to 3 times. The tests with the metal oxides impregnated onto the demineralized char demonstrated that both Ca and Fe oxides enabled better catalytic activity for tar removal than Na and Mg oxides. This study clarified as well that the viable operating conditions for tar removal in a char bed were at 1100 °C with an excessive air ratio (ER) of 0.04 and gas residence time above 1.3 s.

Coal topping gasification refers to a process that extracts the volatiles contained in coal into gas and tar rich in chemical structures in advance of gasification. The technology can be implemented in a reactor system coupling a fluidized bed pyrolyzer and a transport bed gasifier in which coal is first pyrolyzed in the fluidized bed before being forwarded into the transport bed for gasification. The present article is devoted to investigating the pyrolysis of lignite and bituminite in a fluidized bed reactor. The results showed that the highest tar yield appeared at 823 to 923 K for both coals. When coal ash from CFB boiler was used as the bed material, obvious decreases in the yields of tar and pyrolysis gas were observed. Pyrolysis in a reaction atmosphere simulating the pyrolysis gas composition of coal resulted in a higher production of tar. Under the conditions of using CFB boiler ash as the bed material and the simulated pyrolysis gas as the reaction atmosphere, the tar yields for pyrolytic topping in a fluidized bed reactor was about 11.4 wt.% for bituminite and 6.5 wt.% for lignite in dry ash-free coal base.

Biomass containing water of 30–65 wt.% and rich in cellulose, such as various grounds of drinking materials and the lees of spirit and vinegar, is not suitable for biological digestion, and the thermal conversion approach has to be applied to its conversion into bioenergy. The authors have recently worked on converting such biomass into middle heating-value gas via dual fluidized bed gasification (DFBG) integrated with various process intensification technologies. This article is devoted to highlighting those technical ways, including the choice of the superior technical deployment for a DFBG system, the impregnation of Ca onto fuel in fuel drying, the integration of gas cleaning with fuel gasification via two-stage DFBG (T-DFBG), and the decoupling of fuel drying/pyrolysis and char gasification via the decoupled DFBG (D-DFBG). The attained results demonstrated that the superior deployment of bed combination for the DFBG should be a bubbling/turbulent fluidized bed gasifier integrated with a pneumatic riser combustor. In terms of improving efficiency of fuel conversion into combustible gas and suppressing tar generation during gasification, the impregnation of Ca onto fuel exhibited distinctively high upgrading effect, while both the T-DFBG and D-DFBG were also demonstrated to be effective to a certain degree.

A coal gasification technology for producing middle caloric fuel gas using granular coal is urgently required in China considering the huge energy demand required for project development. This work demonstrated the dual-bed gasification technology on a pilot plant (1000 tons of coal/a) mainly consisting of a fluidized-bed gasifier and a pneumatic combustor using the coal with a particle size of less than 20 mm. Simulation was performed with Aspen Plus to investigate the feasibility of producing a middle caloric fuel gas. It was found that, with a bituminite powdered coal as fuel and air as the gasifying reagent, the pilot plant could operate steadily within a given duration of 16 h. At a gasifier temperature of 900 °C and combustor temperature of 980 °C, a fuel gas with 1680 kcal N−1 m−3 of high heating value (HHV) was produced at an equivalence ratio (ER) of 0.089 (defined as the ratio of the oxygen mole in air supplied in the gasifier to the oxygen mole needed for burning the fed coal completely). The heating value of fuel gas could be enhanced by introducing steam as a supplementary reagent to the gasifier while reducing the air required. Gasification simulation of 10 tons of coal/h indicated that a fuel gas with above 2000 kcal N−1 m−3 of HHV could be obtained with an ER of less than 0.10 and a steam/coal ratio larger than 0.48. The study suggested that dual-bed gasification technology could be employed for producing a middle caloric fuel gas using granular coal with a size of less than 20 mm.

Explicitly, the fuel gasification process refers to a reaction converting a solid fuel into gaseous products, but intrinsically, it involves a series of reactions, including fuel pyrolysis, char gasification, tar reforming/cracking, combustible matter combustion, etc. All of these reactions are mutually interactive and fully coupled in a single gasification reactor (i.e., gasifier) for the major commercial gasification technologies. The decoupling gasification (DCG) mentioned in this paper is based on separating and, in turn, reorganizing at least one of the involved reactions to facilitate or suppress the interactive effects between the separated and other reactions. From this decoupling approach, there is potential to allow for the resulting gasification technology to realize the effects of polygeneration, low emission, high efficiency, good product quality, and wide fuel adaptability. This paper generalizes the decoupling approach into two types: isolating and synergizing. Through correlating technical features with these decoupling approaches, re-analysis of the technology principles is made for a few newly developed gasification technologies based on decoupling of the involved gasification reactions. The typical results obtained in research and development of these technologies at bench or pilot scales were recalled to justify the implicated decoupling principle and consequent benefits. As a consequence, the paper concludes that the decoupling of reactions provides a prospective approach to innovate technologies that enable high-efficiency clean conversion of solid fuels into high-quality products.

The quoted two-stage dual fluidized bed gasification (T-DFBG) devises the use of a two-stage fluidized bed (TFB) to replace the single-stage bubbling fluidized bed gasifier involved in the normally encountered dual fluidized bed gasification (N-DFBG) systems. By feeding fuel into the lower stage of the TFB, this lower stage functions as a fuel gasifier similar to that in the N-DFBG so that the upper stage of the TFB works to upgrade the produced gas in the lower stage and meanwhile to suppress the possible elutriation of fuel particles fed into the freeboard of the lower-stage bed. The heat carrier particles (HCPs) circulated from the char combustor enter first the upper stage of the TFB to facilitate the gas upgrading reactions occurring therein, and the particles are in turn forwarded into the lower stage to provide endothermic heat for fuel pyrolysis and gasification reactions. Consequently, with T-DFBG it is hopeful to increase gasification efficiency and decrease tar content in the produced gas. This anticipation was corroborated through gasifying dry coffee grounds in two 5.0kg/h experimental setups configured according to the principles of T-DFBG and N-DFBG, respectively. In comparison with the N-DFBG case, the test according to T-DFBG increased, the fuel C conversion and cold gas efficiency by about 7% and decreased tar content in the produced gas by up to 25% under similar reaction conditions. Test results demonstrated also that all these upgrading effects via adopting T-DFBG were more pronounced when a Ca-based additive was blended into the fuel.

Process residues, such as coffee and tea grounds, bagasse, vinegar lees, etc., represent a kind of concentrated biomass resources rich in cellulose. They contain water usually of about 60 wt % and are easy to rot to cause serious pollution to groundwater and air. Conversion of them into energy can not only control their induced pollution but also develop their CO2 neutralization function. The present paper concerns the production of middle caloric producer gas from such cellulose-rich process biomass residues. The involved technical process consisted of fuel drying and in turn gasification of the dried fuel in a dual fluidized bed system. Using coffee grounds containing 65 wt % water as a model high water content process residue, the paper found that with fuel drying calcium hydrate (or oxide) can be well-impregnated onto fuel to remarkably increase the gasification reactivity of the fuel and suppress tar evolution with producer gas. Thermal gravitational analysis clarified further that the increase in the gasification reactivity of the fuel was due to enhanced char gasification exclusively. In both scanning electron microscopy−energy dispersive X-ray (SEM−EDX) photographs and X-ray diffraction (XRD) spectrums, it was identified that the impregnated Ca species were present at micro sizes and dispersed uniformly on the matrix of fuel as well as char particles made from the fuel. This indicates essentially the necessary precondition for Ca-base material to catalyze biomass fuel gasification.

Gasification of coal and biomass is in pursuit of the technologies based on dual bed combination and a high-density transport bed. Dual fluidized bed gasification (DFBG) relies on rapidly circulated particles between its combustor and gasifier to provide the endothermic heat required by the gasification. High-density transport bed gasification (HTBG) has to work with a high solid flux and a high particle density inside its gasifier so as to increase the heat reserve in the bed and to suppress tar evolution there. The idea of coupling a moving bed to the bottom section of the riser of a circulating fluidized bed (CFB) was proposed to realize the desired high solid-flux conveying flow inside the riser. Experiments in a 12-m high and 90 mm i.d. riser of the newly configured CFB demonstrated that at superficial gas velocities of about 9.6 m/s, a solid circulation rate as high as 370 kg/(m2 s) and an average solid holdup of about 0.12 in the bottom section of the riser were readily achieved simultaneously for the silica sand particles of 378 μm in Sauter mean diameter. Parametric investigation further clarified that the solid circulation rate and the local solid holdup at the riser bottom of the newly configured CFB were highly dependent on the moving bed aeration and the primary gas velocity of the riser, whereas changing the solid inventory in the system did not greatly affect those two variables. Adoption of a secondary air injection into the riser enabled adjustment of the solid circulation rate within a certain range, showing essentially a complementary means for controlling the gas−solid flow inside the riser of the newly configured CFB.

Various process residues represent a kind of biomass resource already concentrated but containing water as much as 60 wt.%. These materials are generally treated as waste or simply combusted directly to generate heat. Recently, we attempted to convert them into middle caloric gas to substitute for natural gas, as a chemical or a high-rank gaseous fuel for advanced combustion utilities. Such conversion is implemented through dual fluidized bed gasification (DFBG). Concerning the high water content of the fuels, DFBG was suggested to accomplish either with high-efficiency fuel drying in advance or direct decoupling of fuel drying/pyrolysis from char gasification and tar/hydrocarbon reforming. Along with fuel drying, calcium-based catalyst can be impregnated into the fuel, without much additional cost, to increase the fuel's gasification reactivity and to reduce tar formation. This article reports the Ca impregnation method and its resulting effects on gasification reactivity and tar suppression ability. Meanwhile, the principle of directly gasifying wet fuel with decoupled dual fluidized bed gasification (D-DFBG) is also highlighted.

•Waste titanium-bearing furnace slag was converted into high-value SCR catalyst.•A low-cost method was proposed to produce the V−W−Ti SCR catalyst.•Silica and iron impurities were found to be the promoter for SCR of NOx.•Slag-based SCR catalyst exhibited good deNOx activity and stability.Preparing SCR (selective catalytic reduction) catalyst from the titanium-bearing blast furnace slag not only realized the high-value utilization of the slag but also provided a low-cost method for V−W−Ti catalyst production. Titanium dioxide was extracted from titanium-bearing blast furnace slag and used as the carrier of V−W−Ti SCR catalyst. Although with 21% SiO2 and a little Al and Fe impurities, the slag-based SCR catalyst exhibited higher deNOx activity and wider active temperature range than commercial TiO2-based catalysts. Under the conditions of NO = 600 ppm, GHSV (gas hourly space velocity) = 24,000 h−1, NH3/NO = 0.8 and O2 = 3%, the slag-based SCR catalyst exhibited NO conversion of higher than 77% in the temperature range of 250–450 °C. For a test at 300 °C, the slag-based catalyst also showed outstanding catalytic stability in the flue gas containing 2000 ppm SO2 and 10% H2O.Download high-res image (197KB)Download full-size image

By varying concentration of PEG1000 as a structure-directing agent, mesoporous alumina with excellent textural properties was synthesized. The prepared mesoporous alumina displays high thermal stability, as shown by its textural properties at different calcination temperatures of 600–850 °C. Characterization by SEM and TEM revealed that the added PEG surfactant induced the formation of petal-like alumina. XRD results clarified that all samples were amorphous and their peaks were around the peaks of γ-alumina. N2 adsorption–desorption analysis showed that the prepared mesoporous alumina, if with PEG1000 in hydrolysis of aluminum isopropoxide, had excellent textural properties with large specific surface area, high pore volume and suitable pore size. The petal-like structure existing in the alumina samples improved their textural parameters, and the role and influential mechanism of PEG1000 were analyzed.

The performance characteristics of isothermal fluidized bed syngas methanation for substitute natural gas are investigated over a self-made Ni–Mg/Al2O3 catalyst. Via atmospheric methanation in a laboratory fluidized bed reactor it was clarified that the CO conversion varied in 5% when changing the space velocity in 40–120 L·g− 1·h− 1 but the conversion increased obviously by raising the superficial gas velocity from 4 to 12.4 cm·s− 1. The temperature at 823 K is suitable for syngas methanation while obvious deposition of uneasy-oxidizing Cγ occurs on the catalyst at temperatures around 873 K. From a kinetic aspect, the lowest reaction temperature is suggested to be 750 K when the space velocity is 60 L·g− 1·h− 1. Raising the H2/CO ratio of the syngas increased proportionally the CO conversion and CH4 selectivity, showing that at enough high H2/CO ratios the active sites on the catalyst are sufficient for CO adsorption and in turn the reaction with H2 for forming CH4. Introducing CO2 into the syngas feed suppresses the water gas shift and Boudouard reactions and thus increased H2 consumption. The ratio of CO2/CO in syngas should be better below 0.52 because varying the ratio from 0.52 to 0.92 resulted in negligible increases in the H2 conversion and CH4 selectivity but decreased the CH4 yield. Introducing steam into the feed gas affected little the CO conversion but decreased the selectivity to CH4. The tested Ni–Mg/Al2O3 catalyst manifested good stability in structure and activity even in syngas containing water vapor.Controlled by thermodynamics, the realized CO conversion and selectivity to CH4 in syngas methanation in a fluidized bed decreased with rising reaction temperature. At temperature lower than 750 K the kinetic rate was low, so did the CO conversion. Meanwhile, the TPO results revealed that the higher methanation temperature caused the higher carbon deposition and the transformation of the reactive Cβ to the hard-oxidizing Cγ. Therefore, the methanation is thus better to be at temperature between 750 K and 823 K for ensuring both activity and stability of the catalyst.Download full-size image

A Micro Fluidized Bed Reaction Analyzer (MFBRA) was used to study the pyrolysis of biomass in argon. Through on-line pulse feeding of reactant and continuously monitoring the composition changes of gas product, the MFBRA enables the measurement of reaction rates at arbitrary temperatures, the deduction of kinetic parameters and the analysis of reaction mechanism. By applying to biomass pyrolysis this article found that the pyrolysis reaction can finish in about 10 s, which is much shorter than the other literature values obtained in larger fluidized bed reactors but very close to the theoretically anticipated values. The detected evolving sequences of different gas species and the deduced kinetic parameters demonstrate further that the reactions between/among the formed different gas species in pyrolysis prevail to certain degree and there are different pathways for forming the different gas species. The activation energy and pre-exponential factor derived by treating the pyrolysis gas as a single product are 11.77 kJ/mol and 1.45 s−1, which are obviously lower than the literature values measured in thermogravimetric analyzers.

The effects of thermal pretreatment on pyrolysis behavior of Shengli lignite were investigated in a fixed bed reactor. In comparison with raw coal, the thermally pretreated coal has lower content of hydroxyl group and lower ratio of aromatic-H to aliphatic-H. The yield of pyrolysis water is lowered after thermal pretreatment in N2, N2+O2 and CO2 atmospheres. The pretreatment also causes a higher CO2 content in pyrolysis gas, which thus lowers the heating value of the gas. Pretreating the coal in superheated steam raises the tar yield by 3–4 weight percentage points, and the composition of tar varies with the atmosphere and temperature of the pretreatment. The light fraction (with boiling points below 360°C) increased by 27 weight percentage points by pretreatment in 200°C -steam. The pretreatments at 200°C and 250°C in the mixture of steam and simulated flue gas elevate the light oil and phenol oil fractions in tar by 60 and 42 weight percentage points, respectively.

•The two-stage gasification process proposed consists of FB pyrolyzer and fixed bed gasifier.•FB pyrolyzer operated at about 850 °C and in O2 and steam-containing atmosphere.•Char bed layer can remove the tar in fuel gas effectively.•The pilot test fully verified the feasibility of two-stage gasification process.A 50 kg/h autothermal two-stage gasifier, consisting of a fluidized bed (FB) pyrolyzer and a downdraft fixed-bed gasifier, has been designed and built according to our previous laboratory researches. In the experiments, lignite gasification was performed in this innovative two-stage gasifier to demonstrate the process feasibility for clean fuel gas production. The results showed that when keeping the reaction temperatures of the FB pyrolyzer and downdraft fixed bed gasifier respectively at about 860 °C and 1100 °C, the tar content in the produced fuel gas from the two-stage gasifier was effectively lowered to 84 mg/Nm3 and the heating value of fuel gas was close to 4.186 MJ/Nm3. Compared with the tar produced in the FB pyrolyzer, the tar from the downdraft fixed bed gasifier had obviously higher content of light oil components and lower content of heavy components, showing essentially an effective catalytic reforming of tar components by the hot char bed of the downdraft fixed bed gasifier.

Mesoporous MnO2-Fe2O3-CeO2-TiO2 was prepared with sol–gel method and demonstrated to have good low-temperature activity and sulfur-poisoning resistance for selective catalytic reduction (SCR) of NO with NH3 in SO2-containing gases. In comparison with this, the catalyst with the same composition but made according to the conventional impregnation method exhibited obviously lower SO2-poisoning resistance and selectivity to the formation of N2 in the SCR reactions. FTIR analysis of the spent catalysts after SCR reactions for 16 h and 60 h in a SO2-contaning gas demonstrated that there was little difference in the amount of deposited ammonium sulfate over the mesoporous catalyst between the two cases. The mesopore channels existing in the mesoporous catalyst enabled probably a dynamic balance between the formation and decomposition of ammonium sulfate in SCR reactions. This concern was justified through comparing the N2 adsorptions and XPS spectra for the catalysts made with the impregnation and sol–gel methods. The article clarified as well the facilitation effects of introducing Ce and Fe into the mesoporous catalyst on activity, selectivity and SO2-poisoning resistance.

Ni–Mg/Al2O3 catalysts prepared with methods of co-precipitation (CP), homogeneous precipitation (HP) and acid–base pairing (ABP) were tested for syngas methanation at 623–923 K in a stainless steel fixed bed reactor and further characterized to justify their performances. The Ni–Mg/Al2O3 catalysts prepared with CP using NH4OH, NaOH and Na2CO3 as the precipitants followed an activity order of NaOH > NH4OH > Na2CO3. Comparing further with the samples prepared by HP and ABP resulted in an activity order of HP > ABP > CP (NaOH) for syngas methanation under 0.1 MPa. For CO conversion, a transition of reaction control from kinetic dominance to thermodynamic dominance was observed at about 780 K. Performing 20 h continuous tests at 773 K and under 0.1 and 2.5 MPa further verified the stability of the HP, ABP and CP (NaOH) catalysts for syngas methanation. Analyzing the catalysts via H2-TPR clarified that a lower amount of free NiO and a stronger interaction between the dispersed NiO and Al2O3 or MgO ensured better catalytic performance for methanation. The study also identified two types of carbon deposited on the surface of the spent catalysts.